First, the Eagles fixed Bryce Brown's fumbling problem enough to get a draft pick from the Buffalo Bills in a trade. Now they're hoping they've fixed Chris Polk's body enough so Brown won't be missed.

Polk had some nagging issues in his first two years as a pro. But after offseason surgery, he seems ready for as much work as the Eagles can throw his way, and his emergence is one of the main components to watch this summer during training camp, which opens Saturday.

Actually, barring an injury to starting running back LeSean McCoy, who is coming off career highs of 314 carries and 1,607 rushing yards, the backups at that spot probably won't figure prominently in the running game. However, when the Eagles do call someone else's number, you can expect a huge difference from last year, when Polk was limited to 15 touches (11 carries, four receptions) and Darren Sproles was still toiling for the New Orleans Saints.

Sproles is tiny (5-foot-6) and on the north side of 30 years old (31). However, his career hit a new level after arriving in New Orleans in 2011, following six seasons in San Diego.

With the Chargers, Sproles ran the football more than he caught it. With the Saints, it was the other way around, and his numbers were staggering for a player who's never started more than six games in a season.

In 2011, Sproles had the ball in his hands 242 times, counting rushes, receptions, punt returns and kickoff returns. He accumulated 2,696 yards and scored 10 touchdowns. By contrast, McCoy's career-high 366 touches last season produced 2,146 yards and 11 TDs.

Though Sproles' numbers have dwindled since, he's remained remarkably productive as a pass catcher, either out of the backfield or flexed out in the slot. He caught 71 passes for 604 yards and a pair of touchdowns while running 53 times for 220 more yards and two more TDs last season.

With the Eagles?

"We are just trying to get reps and get plays and we are not game-planning anybody," coach Chip Kelly said. "That's the fortunate thing for us, is let's see how much work we can get done, get everybody on film and then when we start to get into the season, we'll start to see how we can deploy our personnel in appropriate manners to win games."

That's the coach's nice way of telling us it's none of our business, that it does no good to reveal exactly how he plans to utilize Sproles.

But it would not be a stretch to imagine the Eagles doing the same things with Sproles that the Saints did, while leaving the bulk of the relief running work to Polk, even if Kelly was in no mood to admit anything this summer.

"All of our running backs are receiving options," he said. "I just clarified that. Everyone thinks Darren Sproles is a receiver. He's a running back and a really, really talented running back."

So is Polk, however.

Restricted by turf toe as a rookie and a shoulder problem last season, Polk has not had a lot of playing experience beyond special teams. However, he's proved to be a force with his limited opportunities, scoring on three of 11 carries last season. He's always been a strong and willing blocker too.

Everything points toward Polk, whose shoulder was repaired over the winter, getting around four carries per game, which might be around the same as Sproles, as Kelly tries to dial back McCoy's workload in an effort to maximize his production and his career.

Polk believes that will happen if he keeps working at mastering situations.

"Just overall knowledge of the position, whether it's being patient between runs, knowing the blocking schemes, knowing who to pick up on the blitz, just learning how to read the defense, determining where you're going to cut," Polk said. "Sell them the store, you know? Even though you know the right A gap is open, don't just run there because they're going to close it when you get there. Just sell it, you know?

"It's something I can learn from watching Darren and Shady [McCoy]," he said.

Getting back into top football shape also is a priority, because Polk still was operating eight to 10 pounds above his desired playing weight of 215 during minicamp. That was because he was limited after his surgery.

Because he enters this summer with no apparent limits, it should be interesting to see how the running game plays out for the Eagles this year, and how the work is divided among McCoy, Sproles, Polk and any other running back — Matthew Tucker is the front-runner — who may force himself into the mix.

CHANGE IN BACKUP PLANS

Eagles running backs combined to carry the ball 400 times last season, but top backup Bryce Brown is no longer with the team. Here is the breakdown from 2013: